In recent years, the application of secondary batteries such as lithium ion secondary batteries have rapidly expanded and the batteries have come to be applied to, for example, storage batteries for automobiles or power storage devices for electric power accumulation combined with the new energy system such as solar batteries or wind power generation. For generating high output, a battery system to which one or a plurality of power storage devices is connected is used. The power storage device is formed by, for example, housing one or a plurality of battery blocks in an exterior case. The battery block is formed by connecting a plurality of unit cells (also referred to as a single battery or a cell, and hereinafter called battery cell simply), which corresponds to an example of a power storage element.
As a method of managing such secondary batteries, PTL 1 below discloses the technology of managing a battery pack including a secondary battery by measuring the time of charging and discharging with the large current under high temperature.